The present invention relates to clinching mechanisms for stapler devices which include movable clinching wings that operate to fold the legs of a staple against a work piece.
Automatic stapler devices are commonly used in modern photocopiers and the like, and it is an important feature of the design of such automatic stapler devices that, after clinching of the legs of a staple, the staple project a minimum distance above and below the upper and lower surfaces respectively of a work piece so as to minimise the impact which the presence of the staple has on the overall thickness of the work piece. This has been achieved by the use of clinching wings which are actuated once a staple has been driven through a work piece to engage, bend and clinch the legs of the staple such that they lie substantially flat against the underside of the work piece. However, stapler devices of this kind are typically loaded with staples of a size to suit a wide range of thicknesses of work piece, and as a result, if a thin work piece is stapled, the clinched legs will be much longer than for a thick work piece, and if the clinched legs are too long, they will overlap, which is undesirable.
PCT/US90/00492 teaches a clinching mechanism which overcomes this problem by using an anvil plate which includes a pair of parallel vertical slots that are arranged in side by side overlapping configuration for receiving the unclinched legs of a staple as they protrude from the underside of the work piece and guiding each leg into engagement with its associate clinching wing. The clinching wings are similarly offset from each other in the vertical plane so as to lie in side-by-side planes so that upon rotation of the clinching wings towards the work piece, each leg of the staple is bent into its associated slot and the two legs are brought to lie flat against the work piece parallel to each other, thereby allowing the legs to pass one another as necessary. The arrangement has the drawback, however, that there is a high likelihood that the legs might move laterally of the clinching wings during clinching, resulting in their overlapping and possibly even jamming the staple in the anvil plate, thereby preventing removal of the work piece from the stapling device. This problem is further exasperated due to the fact the overlap between the slots in the anvil plate must be large in order to accommodate for the wide variety of work piece thicknesses and resulting leg lengths, which could lead to a leg being received in the wrong slot.
U.S. Pat. No. 4,593,847 discloses a clinching mechanism which overcomes this problem by forming the slots in the anvil in parallel spaced apart arrangement and positioning a vertically extending plate between and parallel to the slots, which plate prevents the leg that engages in one slot from being clinched across the other slot. However, this system has the disadvantage that the clinched legs will be spaced apart from each other by at least the thickness of the plate.
Accordingly, there is a need for a clinching mechanism which prevents the legs of the staple from overlapping each other during the clinching operation without imposing a minimum separation between the clinched legs.
According to one aspect of the present invention, there is provided a clinching assembly for guiding and clinching a staple, comprising first, second and third plates arranged in a spaced apart stack with said second plate positioned between said first plate and said third plate, first clinching means located between said first plate and said second plate and operable, in use, to clinch a first staple leg received in a first slot formed by the space between said first plate and said second plate, and second clinching means located between said second plate and said third plate and operable, in use, to clinch a second staple leg received in a second slot formed in the space between said second plate and said third plate, wherein said first and third plates have at least one aligned edge forming an anvil surface of the clinching assembly, and said second plate is movable relative to said first and third plates between a first aligned position in which it has an edge aligned with said anvil surface so as to prevent interference between the staple legs as they engage in their respective slots, and a second retracted position in which said edge is withdrawn from said anvil surface so as, in use, to be at least partially retracted from between said inserted staple legs.
The present invention further provides a method of clinching a staple comprising the steps of inserting the staple legs through a work piece into a clinching assembly on opposite sides of a guide plate, at least partially retracting the guide plate from between the unclenched staple legs and then clinching the staple legs.
More particularly, the invention provides a method in which the face of an anvil composed of three spaced apart and stacked plates is driven against one side of a workpiece, a staple is pressed through from the other side of the work piece so that the legs engage in apertures on opposite sides of the middle of said stack plates which forms said guide plate, said guide plate is retracted relative to the side plates, clinching means are actuated to clinch the staple legs against the work piece, the anvil is withdrawn from the workpiece and the guide plate is returned to its original position relative to said side plates.
A clinching assembly and method of use thereof in accordance with the invention has the advantage that the legs of the staples are kept separated when they are inserted into the assembly by the second plate, thereby preventing interference therebetween and in particular preventing the possibility of their crossing over, whilst allowing the legs to be clinched into close alignment with each other and the crown of the staple, thereby resulting in a staple which is much more compact.
Preferably, the clinching means have clinching surfaces which cooperating with the staple legs to develop a camming action therewith that urges the legs laterally towards each other and the staple crown during clinching. In the preferred embodiment, this is achieved by making the clinching surfaces inclined towards each other, but they may also have curved surfaces or the like.
The distance through which the second plate should be moveable relative to the first and third plates, that is the distance between the aligned and the retracted positions of the second plate, is dependant upon the distance which the unclinched staple legs protrude through the work piece to be stapled. The second plate is retracted in order to allow the clinched staple legs to be pressed in close alignment with each other in the final stages of the clinching operation whilst still to be kept separate during the initial bending so as to prevent their overlapping. Accordingly, if the staple legs are particularly long, the second plate may be designed to be retracted further than if the legs are short, it being important merely that the clinched legs are closely aligned with the staple crown but not overlapping in the direction perpendicular to the staple crown. It has been found that a movement of the second plate of less than or equal to 3 mm provides acceptable results for a good range of staple sizes and work pieces.
The clinching means are preferably disposed in mirror image configuration on either side of the second plate and include clinching wings that are pivotally mounted to the first and third plates respectively and which have a curved surface against which an actuating lever associated with each clinching wing engages, each actuating lever pressing against said surface of its associated clinching wing to move it to its clinched position. The actuating levers are advantageously themselves pivotally mounted on their associated plates and are biased by torsion springs into operating engagement with their clinching wings.
Locking means may then be provided, preferably in the form of protrusions on the second plate, which restrain the actuating levers against the force of the biasing means so as to lock the clinching wings in their unclinched position. It is particularly advantageous for the locking means to be so realised as protrusions on the second plate which release the actuating levers to operate the clinching wings when the second plate is retracted, since automatic operation of the clinching wings is thereby achieved in a particularly simple and effective manner.
In the preferred embodiment, the clinching wings each have a lever arm that protrudes laterally from the plates and is engageable to rotate its clinching wings from its clinched to its unclinched position against the force of the biasing spring.
The plates are preferably generally rectangular and are biased into alignment with each other, preferably by means of a spring that engages simultaneously into apertures formed in the three plates that are aligned when the edges of the plates which form the anvil surface are aligned.
The plates are preferably slidably mounted in a housing by means of bushes that are slidable along bars fixed in the housing and which have studs that engage in openings in the plates. The second plate can then be made to be movable to a limited degree relative to the first and third plates in a particularly simple manner by constraining the first and third plates to move with the bushes by making their openings a tolerance fit on the studs and elongating the opening in the second plate to allow it to move to a limited degree relative to the bushes and hence the first and third plates. This arrangement provides a particularly simple anchoring system for the plates whilst still allowing the necessary inter-movements between the plates for proper operation of the invention
Other developments and advantages of the invention are provided below.
In order that the invention may be well understood, there will now be described an embodiment thereof, given by way of example, reference being made to the accompanying drawings, in which: